Many many years ago I was in a solder assembly class in the Western Electric Corporate Engineering Center and the instructor took a three foot length of Sn60Pb40 solder wire off a roll and wound one end off a nail at the top of the blackboard and wound the other end around a small weight and left it hang off the backboard.  He took a chalk and placed a mark on the blackboard where the bottom of the weight was.  He then continued his lecture and every 15 minutes made another mark on the blackboard where the bottom of the weight was.  I don't remember exactly how long his lecture was but it was a 2 hour class.  While he was talking before the class was over we heard a crash and saw that the weight had fallen to the floor and the solder wire had broke somewhere near the middle where its cross section was reduced due to gravity acting on the ductile metal.  He then finished his lecture about mechanical properties of solder and how when you put a mechanical stress on it you will get some ductile flow but when you exceed the yield strength of the solder it will crack and the cracks will occur at the weakest area (i.e., where the cross section is reduced).  He also indicated that in the next class we would cross section the broken ends of the solder wire and what we would find is that the besides the break occurring at the reduced cross sectional area where the stress would be concentrated we'd also find that the break or crack would be at grain boundries.

Regards,
George
George M. Wenger
Failure Signature & Characterization Lab LLC
609 Cokesbury Road, High Bridge, NJ 08829
(908) 638-8771 Home  (732) 309-8964 Mobile
E-mail [log in to unmask]
[log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Kelly
Sent: Wednesday, August 06, 2014 3:15 PM
To: [log in to unmask]
Subject: Re: [TN] SJ fracture signature

Hi George,
Would you mind elaborating on  "mechanical overstress" - I have not heard that term or description before. Thanks. Steve Kelly

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Wenger, George M. [Contractor]
Sent: August-06-14 3:02 PM
To: [log in to unmask]
Subject: Re: [TN] SJ fracture signature

Hi Chris,

I don't think that EDS maps will tell you anything more than you can obtain from the optical photomicrographs of the cross section.  Looks like a typical solder joint mechanical overstress.  It certainly isn't a brittle fracture at a solder/IMC interface that one might expect after a sudden impact or drop test.

Regards,
George
George M. Wenger
Failure Signature & Characterization Lab LLC
609 Cokesbury Road, High Bridge, NJ 08829
(908) 638-8771 Home  (732) 309-8964 Mobile E-mail [log in to unmask] [log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
Sent: Wednesday, August 06, 2014 2:49 PM
To: [log in to unmask]
Subject: [TN] SJ fracture signature

We see hundreds of cracked solder joints every year, but I can't say that I've ever seen one quite like this.  I have some suspicions, but I'll keep them to myself, as to not prejudice the crowd.
EDS maps are forthcoming.

This is a caught in-the-wild field failure of a 48-pin BGA Reballed to SnPb ENIG on board side Ni barrier on component side

http://stevezeva.homestead.com/45268-1.JPG

http://stevezeva.homestead.com/45268-2.JPG

http://stevezeva.homestead.com/45268-8.JPG

Thoughts?  And Thanks to Steve!


Chris Mahanna
President, Technical Manager
Robisan Laboratory Inc.


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________